U.S. patent application number 13/498348 was filed with the patent office on 2012-07-19 for structural steel material and steel structure with high corrosion resistance.
This patent application is currently assigned to JFE STEEL CORPORATION. Invention is credited to Toshiyuki Hoshino, Isamu Kage, Shinichi Miura, Masatsugu Murase.
Application Number | 20120183431 13/498348 |
Document ID | / |
Family ID | 43826422 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120183431 |
Kind Code |
A1 |
Miura; Shinichi ; et
al. |
July 19, 2012 |
STRUCTURAL STEEL MATERIAL AND STEEL STRUCTURE WITH HIGH CORROSION
RESISTANCE
Abstract
A structural steel material contains C: 0.020% or more and less
than 0.140%, Si: 0.05% or more and 2.00% or less, Mn: 0.20% or more
and 2.00% or less, P: 0.005% or more and 0.030% or less, S: 0.0001%
or more and 0.0200% or less, Al: 0.001% or more and 0.100% or less,
Cu: 0.10% or more and 1.00% or less, Ni: 0.10% or more and less
than 0.65%, and W: 0.05% or more and 1.00% or less, and one or both
of Nb: 0.005% or more and 0.200% or less and Sn: 0.005% or more and
0.200% or less, the balance being iron and unavoidable
impurities.
Inventors: |
Miura; Shinichi; (Tokyo,
JP) ; Kage; Isamu; (Tokyo, JP) ; Murase;
Masatsugu; (Tokyo, JP) ; Hoshino; Toshiyuki;
(Tokyo, JP) |
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
|
Family ID: |
43826422 |
Appl. No.: |
13/498348 |
Filed: |
September 28, 2010 |
PCT Filed: |
September 28, 2010 |
PCT NO: |
PCT/JP2010/067310 |
371 Date: |
March 27, 2012 |
Current U.S.
Class: |
420/83 ; 420/91;
420/92 |
Current CPC
Class: |
C22C 38/06 20130101;
C22C 38/008 20130101; C22C 38/04 20130101; C22C 38/08 20130101;
C22C 38/16 20130101; C22C 38/02 20130101; C21D 6/008 20130101; C22C
38/001 20130101; C21D 6/005 20130101; C22C 38/12 20130101; C22C
38/60 20130101; C22C 38/14 20130101; C22C 38/002 20130101 |
Class at
Publication: |
420/83 ; 420/92;
420/91 |
International
Class: |
C22C 38/42 20060101
C22C038/42; C22C 38/08 20060101 C22C038/08; C22C 38/16 20060101
C22C038/16 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2009 |
JP |
2009-226164 |
Aug 24, 2010 |
JP |
2010-187057 |
Claims
1. A structural steel material comprising, in terms of mass %, C:
0.020% or more and less than 0.140%, Si: 0.05% or more and 2.00% or
less, Mn: 0.20% or more and 2.00% or less, P: 0.005% or more and
0.030% or less, S: 0.0001% or more and 0.0200% or less, Al: 0.001%
or more and 0.100% or less, Cu: 0.10% or more and 1.00% or less,
Ni: 0.10% or more and less than 0.65%, W: 0.05% or more and 1.00%
or less, and one or both of Nb: 0.005% or more and 0.200% or less
and Sn: 0.005% or more and 0.200% or less, the balance being iron
and unavoidable impurities.
2. The structural steel material according to claim 1, comprising,
in terms of mass %, Nb: 0.005% or more and 0.200% or less and Sn:
0.005% or more and 0.200% or less.
3. The structural steel material according to claim 1, further
comprising, in terms of mass %, Cr: more than 0.1% and 1.0% or
less.
4. The structural steel material according to claim 1, further
comprising, in terms of mass %, at least one selected from the
group consisting of Co: 0.01% or more and 1.00% or less, Mo: 0.005%
or more and 1.000% or less, Sb: 0.005% or more and 0.200% or less,
and REM: 0.0001% or more and 0.1000% or less.
5. The structural steel material according to claim 1, further
comprising, in terms of mass %, at least one selected from the
group consisting of Ti: 0.005% or more and 0.200% or less, V:
0.005% or more and 0.200% less, Zr: 0.005% or more and 0.200% or
less, B: 0.0001% or more and 0.0050% or less, and Mg: 0.0001% or
more and 0.0100% or less.
6. The structural steel material according to claim 1, wherein a
weld cracking parameter Pcm defined by Formula (1) below is 0.25
mass % or less:
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5.t-
imes.[B] (1) where [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V],
and [B] represent contents (mass %) of respective elements.
7. A steel structure comprising the structural steel material
according to claim 1.
8. The structural steel material according to claim 2, further
comprising, in terms of mass %, Cr: more than 0.1% and 1.0% or
less.
9. The structural steel material according to claim 2, further
comprising, in terms of mass %, at least one selected from the
group consisting of Co: 0.01% or more and 1.00% or less; Mo: 0.005%
or more and 1.000% or less, Sb: 0.005% or more and 0.200% or less,
and REM: 0.0001% or more and 0.1000% or less.
10. The structural steel material according to claim 3, further,
comprising, in terms of mass %, at least one selected from the
group consisting of Co: 0.01% or more and 1.00% or less, Mo: 0.005%
or more and 1.000% or less, Sb: 0.005% or more and 0.200% or less,
and REM: 0.0001% or more and 0.1000% or less.
11. The structural steel material according to claim 2, further
comprising, in terms of mass %, at least one selected from the
group consisting of Ti: 0.005% or more and 0.200% or less, V:
0.005% or more and 0.200% or less, Zr: 0.005% or more and 0.200% or
less, B: 0.0001% or more and 0.0050% or less, and Mg: 0.0001% or
more and 0.0100% or less.
12. The structural steel material according to claim 3, further
comprising, in terms of mass %, at least one selected from the
group consisting of Ti: 0.005% or more and 0.200% or less, V:
0.005% or more and 0.200% or less, Zr: 0.005% or more and 0.200% or
less, B: 0.0001% or more and 0.0050% or less, and Mg: 0.0001% or
more and 0.0100% or less.
13. The structural steel material according to claim 4, further
comprising, in terms of mass %, at least one selected from the
group consisting of Ti: 0.005% or more and 0.200% or less, V:
0.005% or more and 0.200% or less, Zr: 0.005% or more and 0.200% or
less, B: 0.0001% or more and 0.0050% or less, and Mg: 0.0001% or
more and 0.0100% or less.
14. The structural steel material according to claim 2, wherein a
weld cracking parameter Pcm defined by Formula (1) below is 0.25
mass % or less:
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15[V]/10+5.ti-
mes.[B] (1) where [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], and
[B] represent contents (mass %) of respective elements.
15. The structural steel material according to claim 3, wherein a
weld cracking parameter Pcm defined by Formula (1) below is 0.25
mass % or less:
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5.t-
imes.[B] (1) where [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V],
and [B] represent contents (mass %) of respective elements.
16. The structural steel material according to claim 4, wherein a
weld cracking parameter Pcm defined by Formula (1) below is 0.25
mass % or less:
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[MO]/15+[V]/10+5.t-
imes.[B] (1) where [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V],
and [B] represent contents (mass %) of respective elements.
17. The structural steel material according to claim 5, wherein a
weld cracking parameter Pcm defined by Formula (1) below is 0.25
mass % or less:
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5.t-
imes.[B] (1) where [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V],
and [B] represent contents (mass %) of respective elements.
18. A steel structure comprising the structural steel material
according to claim 2.
19. A steel structure comprising the structural steel material
according to claim 3.
20. A steel structure comprising the structural steel material
according to claim 4.
Description
RELATED APPLICATIONS
[0001] This is a .sctn.371 of International Application No.
PCT/JP2010/067310, with an international filing date of Sep. 28,
2010 (WO 2011/040621A1, published Apr. 7, 2011), which is based on
Japanese Patent Application Nos. 2009-226164, filed Sep. 30, 2009,
and 2010-187057, filed Aug. 24, 2010, the subject matter of which
is incorporated by reference.
TECHNICAL FIELD
[0002] This disclosure generally relates to steel structures such
as bridges that are used outdoors, in particular, to a steel
material and a steel structure suitable for use in parts required
to exhibit atmospheric corrosion resistance in a high air-borne
salt environment such as a coastal environment.
BACKGROUND
[0003] Conventionally, weathering steel has been used in outdoor
steel structures such as bridges. Weathering steel is a steel
material that exhibits a significantly low corrosion rate in an
atmospheric environment because surfaces thereof are covered with a
highly protective rust layer in which alloy elements such as Cu, P,
Cr, and Ni are concentrated. Bridges that use paintless weathering
steel are known to frequently withstand decades of service owing to
the steel's high atmospheric corrosion resistance.
[0004] However, it has been known that in an environment with a
high amount of air-borne salt such as a coastal environment, the
highly protective rust layer rarely forms and practical atmospheric
corrosion resistance is rarely achieved.
[0005] According to "Joint study report on use of weathering steel
material in bridges [Taikosei kozai no kyouryou heno tekiyou ni
kansuru kyodo kenkyu hokokusho] (XX)," No. 88, March 1993, Public
Works Research Institute in Ministry of Construction, Kozai Club,
and Japan Bridge Association, conventional weathering steel (JIS G
3114: atmospheric corrosion resistant steel for welded structure)
can be used paintless only in the regions where the amount of
air-borne salt is 0.05 mgNaCl/dm.sup.2/day (hereinafter, the unit
(mgNaCl/dm.sup.2/day) may be denoted as mdd) or less. Accordingly,
in an environment where the amount of air-borne salt is high such
as a coastal environment, regular steel material (JIS G 3106:
rolled steel material for welded structure) subjected to an
anticorrosive treatment such as coating has been used. Note that dm
denotes decimeter.
[0006] With regard to coating, coating films deteriorate with lapse
of time and require regular maintenance and repair. In addition,
the rise of labor cost and need for recoating add to the
difficulty. Due to these reasons, presently, steel materials that
can be used paintless are desired and steel materials that can be
used paintless are in high demand.
[0007] Under such a trend, steel materials that contain various
alloy elements, in particular, a large amount of Ni, have been
developed as a steel material that can be used paintless in an
environment where the amount of air-borne salt is high, such as a
coastal environment.
[0008] For example, Japanese Patent No. 3785271 (Japanese
Unexamined Patent Application Publication No. 11-172370) discloses
a highly corrosion-resistant steel material containing Cu and 1 wt
% or more of Ni as the elements that improve atmospheric corrosion
resistance.
[0009] Japanese Patent No. 3846218 (Japanese Unexamined Patent
Application Publication No. 2002-309340) discloses a steel material
having high atmospheric corrosion resistance and containing 1 mass
% or more of Ni and Mo.
[0010] Japanese Patent No. 3568760 (Japanese Unexamined Patent
Application Publication No. 11-71632) discloses a steel material
having high atmospheric corrosion resistance and containing Cu and
Ti in addition to Ni.
[0011] Japanese Unexamined Patent Application Publication No.
10-251797 discloses a steel material for welded structure, the
steel material containing a large amount of Ni in addition to Mo,
Sn, Sb, P, etc.
[0012] Japanese Unexamined Patent Application Publication No.
2007-254881 does not mention atmospheric corrosion resistance in an
environment containing a high amount of air-borne salt such as a
coastal environment, but discloses a corrosion-resistant steel
material for ships, the corrosion-resistant steel material
containing W and Cr in addition to Sb, Sn, Ni, etc., for use as a
corrosion-resistant material used in a severe corrosion environment
where materials are directly exposed to splash of seawater, such as
ballast tanks of ships.
[0013] However, when the Ni content is increased as in JP '271 and
JP '218, the price of the steel material increases due to the
alloying cost.
[0014] In JP '760, the Ni content is suppressed to a low level and
Cu and Ti are added.
[0015] A steel material that contains an increased amount of Ni as
well as Cu, Mo, Sn, Sb, P, and the like such as one disclosed in JP
'797 costs high due to the increase in alloying cost and has low
weldability due to a high P content.
[0016] The steel material disclosed in JP '881 has a different
usage and a different required atmospheric corrosion resistance. No
mention is made as to the atmospheric corrosion resistance in an
environment with a high amount of air-borne salt such as a coastal
environment.
[0017] It could therefore be helpful to provide a structural steel
material and a steel structure that have high atmospheric corrosion
resistance at low cost.
SUMMARY
[0018] We provide a structural steel material including, in terms
of mass %, C: 0.020% or more and less than 0.140%, Si: 0.05% or
more and 2.00% or less, Mn: 0.20% or more and 2.00% or less, P:
0.005% or more and 0.030% or less, S: 0.0001% or more and 0.0200%
or less, Al: 0.001% or more and 0.100% or less, Cu: 0.10% or more
and 1.00% or less, Ni: 0.10% or more and less than 0.65%, W: 0.05%
or more and 1.00% or less, and one or both of Nb: 0.005% or more
and 0.200% or less and Sn: 0.005% or more and 0.200% or less, the
balance being iron and unavoidable impurities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a graph showing the relationship between the steel
types (steel type Nos. A to X) shown in Table 1 and the average
decrease in thickness.
[0020] FIG. 2 is a diagram showing conditions and a cycle of a
corrosion test.
DETAILED DESCRIPTION
[0021] To address the problems described above, the composition of
the steel material was investigated from the standpoint of
atmospheric corrosion resistance in a high air-borne salt
environment. As a result, we found that the atmospheric corrosion
resistance of a steel material in a high air-borne salt environment
improves when W and Sn and/or Nb are contained in a base steel
containing Cu and Ni.
[0022] FIG. 1 shows the results of a wet and dry cyclic corrosion
test conducted on steel materials containing components shown in
Table 1. The wet and dry cyclic corrosion test was conducted as
follows. A test specimen 35 mm.times.35 mm.times.5 mm in size was
taken from each steel material and a diluted solution of artificial
seawater was applied to the test specimen once a week during a dry
process so that the amount of salt adhering to the surface was 0.2
mdd. A 24-hour cycle including 11 hours of the dry process at a
temperature of 40.degree. C. and a relative humidity of 40% RH and
11 hours of a wet process at 25.degree. C. and a relative humidity
of 95% RH with 1 hour of transition time was performed for 12 weeks
(84 cycles). The test specimen was immersed in an aqueous solution
prepared by adding hexamethylenetetramine to hydrochloric acid to
conduct derusting and then weighed. The decrease in thickness
(unit: .mu.m) is an average decrease in thickness at one side of
the test specimen and determined by obtaining the difference
between the initial weight and the weight measured as above and
then dividing the result by a surface area of the tested portion of
the test specimen. The same test was conducted three times for each
steel type. The average of the three measurements is marked by a
solid circle in FIG. 1 and the minimum and maximum values are
indicated by an error bar.
[0023] It was known that 0.2 mdd of adhered salt in this corrosion
test is equivalent to about 0.5 mdd in terms of the amount of
air-borne salt. The environment with about 0.5 mdd of air-born salt
corresponds to a high air-borne salt environment such as a coastal
environment.
[0024] The amount of corrosion 100 years later is determined by
extrapolation from the average decrease in thickness determined by
this test. The average decrease in thickness 100 years later is 0.5
mm or less, i.e., rust caused by exfoliation of layers can be
prevented, if the average decrease in thickness observed during the
period of the corrosion test is 14 .mu.m or less.
[0025] In general, whether paintless weathering steel can be used
in bridges is determined by whether the decrease in thickness 100
years later is 0.5 mm or less. The steel materials can be used as
paintless weathering steel for use in bridges if the average
decrease in thickness is 14 .mu.m or less in this atmospheric
corrosion resistance test.
[0026] Thus, in FIG. 1, steel materials with an average decrease in
thickness of 14 .mu.m or less were judged as having high
atmospheric corrosion resistance.
[0027] The results in FIG. 1 show that the steel (steel type D)
composed of a base steel (steel type R), W, and Nb and the steel
(steel type C) composed of the same base steel, W, and Sn had an
average decrease in thickness less than 14 .mu.m and thus have
significantly high atmospheric corrosion resistance compared to a
conventional weathering steel (steel type Q), an ordinary steel
(steel type S), and steels containing other combinations of
elements (steel types A, B, and E to P). Comparison between the
steel types C and D and the steel type T with a high Ni content
indicates that the atmospheric corrosion resistance of the steel
types C and D is superior to that of the steel type T.
[0028] The reasons why the steel types C and D exhibited high
atmospheric corrosion resistance despite a low Ni content are
believed as follows.
[0029] Steel types C and D are each a steel that has a low Ni
content and contains Cu, W, Nb and/or Sn. Cu and Ni densify the
rust layer and prevent chloride ions which are corrosion
accelerating factors from permeating through the rust layer and
reaching the base iron. W forms a complex oxide with Fe at an anode
portion near the interface between the rust layer and the base iron
to thereby suppress an anode reaction. Moreover, W exhibits
selective permeability for cations by forming tungstic ions
distributed in the rust layer and prevents the chloride ions, i.e.,
corrosion accelerating factors, from permeating through the rust
layer and reaching the base iron. Nb is concentrated at the anode
portion near the interface between the rust layer and the base iron
and suppresses the anode reaction and cathode reaction. Sn, as with
Nb, is concentrated at the anode portion near the interface between
the rust layer and the base iron and suppresses the anode reaction
and cathode reaction. However, these effects are insufficient if
these elements are contained alone. The synergetic effect of
incorporation of Cu, Ni, W, Nb and/or Sn presumably significantly
improves the corrosion suppressing effects of Cu, Ni, W, Nb, and
Sn.
[0030] In particular, when a steel (steel type V or W) containing
Nb or Sn in addition to a steel (steel type U) containing Cu, Ni,
and W is compared with a steel (steel type X) containing both Nb
and Sn in addition to the steel type U, the atmospheric corrosion
resistance of the steel type X is far higher than that of the steel
types V and W.
[0031] As seen in the steel types C, D, V, and W, our desired
effects are achieved as long as at least one of Nb and Sn is
contained. However, incorporation of both Nb and Sn more notably
improves the atmospheric corrosion resistance as demonstrated by
steel type X.
[0032] We thus provide: [0033] [1] A structural steel material with
high corrosion resistance including, in terms of mass %, C: 0.020%
or more and less than 0.140%, Si: 0.05% or more and 2.00% or less,
Mn: 0.20% or more and 2.00% or less, P: 0.005% or more and 0.030%
or less, S: 0.0001% or more and 0.0200% or less, Al: 0.001% or more
and 0.100% or less, Cu: 0.10% or more and 1.00% or less, Ni: 0.10%
or more and less than 0.65%, W: 0.05% or more and 1.00% or less,
and one or both of Nb: 0.005% or more and 0.200% or less and Sn:
0.005% or more and 0.200% or less, the balance being iron and
unavoidable impurities. [0034] [2] The structural steel material
with high corrosion resistance as described in [1], including, in
terms of mass %, Nb: 0.005% or more and 0.200% or less and Sn:
0.005% or more and 0.200% or less. [0035] [3] The structural steel
material with high corrosion resistance as described in [1] or [2],
further including, in terms of mass %, Cr: more than 0.1% and 1.0%
or less. [0036] [4] The structural steel material with high
corrosion resistance as described in any one of [1] to [3], further
including, in terms of mass %, at least one selected from Co: 0.01%
or more and 1.00% or less, Mo: 0.005% or more and 1.000% or less,
Sb: 0.005% or more and 0.200% or less, and REM: 0.0001% or more and
0.1000% or less. [0037] [5] The structural steel material with high
corrosion resistance as described in any one of [1] to [4], further
including, in terms of mass %, at least one selected from Ti:
0.005% or more and 0.200% or less, V: 0.005% or more and 0.200% or
less, Zr: 0.005% or more and 0.200% or less, B: 0.0001% or more and
0.0050% or less, and Mg: 0.0001% or more and 0.0100% or less.
[0038] [6] The structural steel material with high corrosion
resistance as described in any one of [1] to [5], in which a weld
cracking parameter Pcm defined by formula (1) below is 0.25 mass %
or less:
[0038]
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5.-
times.[B] (1) [0039] where [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo],
[V], and [B] represent contents (mass %) of respective elements.
[0040] [7] A steel structure including the structural steel
material with high corrosion resistance as described in any one of
[1] to [6].
[0041] In this description, % of the component of the steel is mass
%. "High atmospheric corrosion resistance" means that the
structural steel material satisfies in practice the high
atmospheric corrosion resistance required in high air-borne salt
environment of 0.5 mdd or less.
[0042] A structural steel material and a steel structure having
high atmospheric corrosion resistance are obtained at low cost. The
structural steel material is low-cost since plural elements
effective for improving the atmospheric corrosion resistance are
contained without incorporation of large amounts of expensive
elements such as Ni, has practical weldability, and exhibits high
atmospheric corrosion resistance in a high air-borne salt
environment such as a coastal environment. A particularly notable
effect is exhibited in a high air-borne salt environment where the
amount of air-borne salt exceeds 0.05 mdd. However, the upper limit
of the amount of air-borne salt is preferably 0.5 mdd or less and
the upper limit of the amount of salt adhered is preferably 0.2 mdd
or less.
[0043] Our steels and structures will now be described in
detail.
C: 0.020% or More and Less than 0.140%
[0044] Carbon is an element that improves the strength of a
structural steel material. The carbon content needs to be 0.020% or
more to ensure a required strength. At a C content of 0.140% or
more, weldability and toughness are deteriorated. Accordingly, the
C content is 0.020% or more and less than 0.140% and preferably in
a range of 0.060 to 0.100%.
Si: 0.05% or More and 2.00% or Less
[0045] Silicon acting as a deoxidizing agent during steel making
and an element that improves the strength of the structural steel
material to ensure the required strength needs to be contained in
an amount of 0.05% or more. Incorporation of excess Si exceeding
2.00% significantly deteriorates toughness and weldability.
Accordingly, the Si content is 0.05% or more and 2.00% or less and
is preferably in a range of 0.10 to 0.80%.
Mn: 0.20% or More and 2.00% or Less
[0046] Manganese is an element that improves the strength of the
structural steel material and 0.20% or more of Mn needs to be
contained to ensure a required strength. In contrast, the toughness
and weldability are deteriorated if Mn is contained exceeding
2.00%. Accordingly, the Mn content is 0.20% or more and 2.00% or
less and preferably in a range of 0.20 to 1.50%.
P: 0.005% or More and 0.030% or Less
[0047] Phosphorus is an element that improves the atmospheric
corrosion resistance of the structural steel material. 0.005% or
more of P needs to be contained to achieve this effect. However, if
more than 0.030% of P is contained, weldability is deteriorated.
Accordingly, the P content is 0.005% or more and 0.030% or less and
preferably in a range of 0.005 to 0.025%.
S: 0.0001% or More and 0.0200% or Less
[0048] At a sulfur content exceeding 0.0200%, weldability and
toughness are deteriorated. If the S content is reduced to less
than 0.0001%, production cost will increase. Accordingly, the S
content is 0.0001% or more and 0.0200% or less and preferably in a
range of 0.0003 to 0.0050%.
Al: 0.001% or More and 0.100% or Less
[0049] Aluminum is an element needed in deoxidization during steel
making. The Al content needs to be 0.001% or more to achieve this
effect. At an Al content exceeding 0.100%, however, weldability is
adversely affected. Thus, the Al content is 0.001% or more and
0.100% or less and preferably in a range of 0.010 to 0.050%.
Acid-soluble Al was measured in determining the Al content.
Cu: 0.10% or More and 1.00% or Less
[0050] Copper reduces the size of rust grains to help form a dense
rust layer and thus has an effect of improving the atmospheric
corrosion resistance of the structural steel material. This effect
is achieved when the Cu content is 0.10% or more. At a Cu content
exceeding 1.00%, the cost will rise due to the increased
consumption of Cu. Accordingly, the Cu content is 0.10% or more and
1.00% or less and preferably in a range of 0.20 to 0.50%.
[0051] JP '881 relates to a weathering steel material for ships.
Under current technology, the lifetime of corrosion resistant
coating of ballast tanks of ships (typically 10 years) is half that
of ships (20 years) and the atmospheric corrosion resistance of the
remaining 10 years is retained by maintenance and repair of the
coating. An object of the weathering steel material described in JP
'881 is to offer high atmospheric corrosion resistance unaffected
by the surface condition of the steel material under a severe
corrosive environment where the material is directly exposed to
seawater and splash thereof such as ballast tanks of ships so that
the period up to which the maintenance coating is required can be
extended, and to alleviate the load of the maintenance coating. In
contrast, our structural steel material is used in outdoor steel
structures such as bridges and an object is to achieve a decrease
in thickness of 0.5 mm or less 100 years later in a high air-borne
salt environment such as a coastal environment. The environment in
which the steel material is used and the object significantly
differ from those of the steel material described in JP '881.
Accordingly, whereas the steel material described in JP '881 does
not have to contain Cu, our steel material needs to contain Cu to
help form a dense rust and improve the atmospheric corrosion
resistance of the steel material. Thus, the Cu content is 0.10% or
more.
Ni: 0.10% or More and Less than 0.65%
[0052] Nickel reduces the size of rust grains to help form a dense
rust layer and has an effect of improving the atmospheric corrosion
resistance of the structural steel material. The Ni content needs
to be 0.10% or more to fully bring this effect. At a Ni content of
0.65% or more, the cost will rise due to the increased consumption
of Ni. Accordingly, the Ni content is 0.10% or more and less than
0.65% and preferably in a range of 0.15 to 0.50%.
W: 0.05% or more and 1.00% or less, Nb: 0.005% or More and 0.200%
or Less and/or Sn: 0.005% or More and 0.200% or Less
[0053] Tungsten is a important element and has an effect of
dramatically improving the atmospheric corrosion resistance of the
steel material in a high air-borne salt environment when contained
in combination with Nb and/or Sn. WO42--elutes as the anode
reaction of the steel material proceeds and distributes itself in
the rust layer to electrostatically prevent chloride ions, i.e.,
corrosion accelerating factors, from permeating through the rust
layer and reaching the base iron. Moreover, compounds containing W
settle on the steel material surface and suppress the anode
reaction of the steel material. The W content needs to be 0.05% or
more to fully bring this effect. At a W content exceeding 1.00%,
the cost will rise due to an increase in consumption of W. Thus,
the W content is 0.05% or more and 1.00% or less and preferably in
a range of 0.10 to 0.70%.
[0054] Niobium is a important element and has an effect of
dramatically improving the atmospheric corrosion resistance of the
steel material in a high air-borne salt environment when contained
in combination with W. Niobium is concentrated at the anode portion
near the interface between the rust layer and the base iron and
suppresses anode reaction and cathode reaction. The Nb content
needs to be 0.005% or more to fully bring this effect. At a Nb
content exceeding 0.200%, the toughness is decreased. Accordingly,
the Nb content is 0.005% or more and 0.200% or less and preferably
in a range of 0.010 to 0.030%.
[0055] Tin is a important element and has an effect of dramatically
improving the atmospheric corrosion resistance of the steel
material in a high air-borne salt environment when contained in
combination with W. Tin helps form an oxide coating film containing
Sn on the steel material surface and suppresses anode reaction and
cathode reaction of the steel material to improve atmospheric
corrosion resistance of the structural steel material. The Sn
content needs to be 0.005% or more to fully bring these effects. At
a Sn content exceeding 0.200%, however, the ductility and toughness
of the steel are deteriorated. Accordingly the Sn content is 0.005%
or more and 0.200% or less and preferably in a range of 0.010 to
0.050%.
[0056] Our desired effects can be achieved as long as one of Nb and
Sn is contained. However, incorporation of both Nb and Sn has an
effect of notably improving atmospheric corrosion resistance. The
reasons why incorporation of both Nb and Sn brings such an effect
are not yet clear. Presumably, conditions (e.g., ambient conditions
such as temperature, relative humidity, and salt concentration in
the rust) under which Nb exhibits a notable effect are different
from conditions under which Sn exhibits a notable effect, and thus
Nb and Sn complement one another in an environment in which the dry
process and the wet process repetitively occur, thereby notably
improving the atmospheric corrosion resistance.
[0057] There is also an advantage that the amounts of Nb and Sn
added can be decreased without deteriorating atmospheric corrosion
resistance in reliably obtaining the required mechanical properties
and weldability of the steel material. Due to these reasons,
incorporation of both Nb and Sn is preferred.
[0058] The balance is Fe and unavoidable impurities.
[0059] Allowable unavoidable impurities are N: 0.010% or less, O:
0.010% or less, and Ca: 0.0010% or less. Calcium contained as an
unavoidable impurity deteriorates the toughness of the weld
heat-affected zone if contained in large amounts and thus the Ca
content is preferably 0.0010% or less.
[0060] In addition to the elements described above, the following
alloy elements may be added as needed.
Cr: More than 0.1% and 1.0% or Less
[0061] Chromium is an element that helps form a dense rust layer by
decreasing the size of rust grains and improves atmospheric
corrosion resistance. The Cr content needs to be more than 0.1% to
fully bring this effect. At a Cr content exceeding 1.0%, the
weldability is degraded. Thus, when Cr is to be contained, the Cr
content is more than 0.1% and 1.0% or less and preferably in a
range of 0.2 to 0.7%.
[0062] At least one selected from Co, Mo, Sb, and rare earth metals
(REM) may be contained for the following reasons.
Co: 0.01% or More and 1.00% or Less
[0063] Cobalt distributes itself in the entire rust layer, reduces
the size of the rust grains to help form a dense rust layer, and
has an effect of improving atmospheric corrosion resistance of the
structural steel material. The Co content needs to be 0.01% or more
to fully bring this effect. At a Co content exceeding 1.00%, the
cost will rise due to an increase in consumption of Co. Thus, when
Co is to be contained, the Co content is 0.01% or more and 1.00% or
less and preferably in a range of 0.10 to 0.50%.
Mo: 0.005% or More and 1.000% or Less
[0064] Molybdenum prevents chloride ions, i.e., corrosion
accelerating factors, from permeating through the rust layer and
reaching the base iron since MoO42--elutes as the anode reaction of
the steel material proceeds and distributes itself in the rust
layer. Moreover, compounds containing Mo settle on the steel
material surface and suppress the anode reaction of the steel
material. The Mo content needs to be 0.005% or more to fully bring
this effect. At a Mo content exceeding 1.000%, the cost will rise
due to an increase in consumption of Mo. Thus, when Mo is to be
contained, the Mo content is 0.005% or more and 1.000% or less and
preferably in a range of 0.100 to 0.500%.
Sb: 0.005% or More and 0.200% or Less
[0065] Antimony is an element that suppresses the anode reaction of
the steel material and hydrogen-generating reaction, which is the
cathode reaction, to thereby improve atmospheric corrosion
resistance of the structural steel material. The Sb content needs
to be 0.005% or more to fully bring this effect. At an Sb content
exceeding 0.200%, the toughness is deteriorated. Accordingly, when
Sb is to be contained, the Sb content is 0.005% or more and 0.200%
or less and preferably in a range of 0.010 to 0.050%.
REM: 0.0001% or More and 0.1000% or Less
[0066] REM distributes itself to the entire rust layer, reduces the
size of the rust grains to help form a dense rust layer, and has an
effect of improving the atmospheric corrosion resistance of the
structural steel material. The REM content needs to be 0.0001% or
more to fully bring this effect. At a REM content exceeding
0.1000%, the effect thereof is saturated. Accordingly, when REM is
to be contained, the REM content is 0.0001% or more and 0.1000% or
less and preferably in a range of 0.0010 to 0.0100%.
[0067] At least one selected from Ti, V, Zr, B, and Mg may be
contained for the following reasons.
Ti: 0.005% or More and 0.200% or Less
[0068] Titanium is an element needed to increase the strength. The
Ti content needs to be 0.005% or more to fully bring this effect.
At a Ti content exceeding 0.200%, the toughness is deteriorated.
Thus, when Ti is to be contained, the Ti content is 0.005% or more
and 0.200% or less and preferably in a range of 0.010 to
0.100%.
V: 0.005% or More and 0.200% or Less
[0069] Vanadium is an element needed to increase the strength. The
V content needs to be 0.005% or more to fully bring this effect. At
a V content exceeding 0.200%, the effect is saturated. Thus, when V
is to be contained, the V content is 0.005% or more and 0.200% or
less and preferably in a range of 0.010 to 0.100%.
Zr: 0.005% or More and 0.200% or Less
[0070] Zirconium is an element needed to increase the strength. The
Zr content needs to be 0.005% or more to fully bring this effect.
At a Zr content exceeding 0.200%, the effect is saturated.
Accordingly, when Zr is to be contained, the Zr content is 0.005%
or more and 0.200% or less and preferably in a range of 0.010 to
0.100%.
B: 0.0001% or More and 0.0050% or Less
[0071] Boron is an element needed to increase the strength. The B
content needs to be 0.0001% or more to fully bring this effect. At
a B content exceeding 0.0050%, the toughness is deteriorated.
Accordingly, when B is to be contained, the B content is 0.0001% or
more and 0.0050% or less and preferably in a range of 0.0005 to
0.0020%.
Mg: 0.0001% or More and 0.0100% or Less
[0072] Magnesium is an element that fixes S in the steel and is
effective for improving the toughness of the weld heat-affected
zone. The Mg content needs to be 0.0001% or more to fully bring
this effect. At a Mg content exceeding 0.0100%, the amounts of
inclusions in the steel increase and the toughness is deteriorated.
Accordingly, when Mg is to be contained, the Mg content is 0.0001%
or more and 0.0100% or less and preferably in a range of 0.0005 to
0.0020%.
Pcm: 0.25 Mass % or Less
[0073] To prevent low-temperature cracking by welding and bring the
preheating temperature during welding operation to a practical
level of 50.degree. C. or less, weld cracking parameter Pcm defined
by the formula below is preferably 0.25 mass % or less and more
preferably 0.20 mass % or less:
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5.times.[-
B]
where [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], and [B]
represent the contents (mass %) of the respective elements.
[0074] The structural steel material having high atmospheric
corrosion resistance is obtained by melting a steel having the
above-described composition by using melting means such as a steel
converter or an electric furnace by an ordinary method and
hot-rolling a slab obtained by ordinary continuous casting or
slabbing to prepare a steel material such as a steel plate, a
shaped steel, a steel plate, or a bar steel. The heating and
rolling conditions may be adequately determined according to the
quality of the material used. A combination of controlled rolling,
accelerated cooling, and a heat treatment such as reheating can be
employed.
[0075] When the structural steel material obtained as such is used
as a structural member of a steel structure, a steel structure
having high atmospheric corrosion resistance in a high air-borne
salt environment such as a coastal environment can be obtained.
EXAMPLES
[0076] Steels having chemical compositions shown in Table 2 were
melted, heated to 1150.degree. C., hot rolled, and air-cooled to
room temperature to prepare steel plates 6 mm in thickness. Then a
test specimen 35 mm.times.35 mm.times.5 mm in size was taken from
each of the steel plates obtained. The test specimen was subjected
to grinding processing so that the surface had a surface roughness
Ra of 1.6 .mu.m or less. An edge face and a back side were sealed
with a tape and the surface was also sealed with a tape so that the
area of the exposed area was 25 mm.times.25 mm.
[0077] The test specimens obtained as such were subjected to a wet
and dry cyclic corrosion test to evaluate the atmospheric corrosion
resistance.
[0078] A corrosion test employed as the wet and dry cyclic
corrosion test simulated an environment of inside girders not under
eaves which is presumably the severest environment for actual
structures such as bridges. The conditions for the corrosion test
were as follows: One 24-hour cycle included 11 hours of a dry
process at a temperature of 40.degree. C. and a relative humidity
of 40% RH, 1 hour of transition time, 11 hours of a wet process at
a temperature of 25.degree. C. and a relative humidity of 95% RH,
and 1 hour of transition time to simulate the temperature-humidity
cycle of actual environments. A diluted solution of artificial
seawater was applied to the test specimen once a week during the
dry process so that the amount of salt adhering to the test
specimen surface was 0.2 mdd. Under these conditions, 84 cycles of
testing were conducted in 12 weeks. The conditions and the cycle of
the corrosion test are schematically illustrated in FIG. 2. After
completion of the corrosion test, the test specimen was immersed in
an aqueous solution of hexamethylenetetramine in hydrochloric acid
to remove rust and weighed, and an average decrease in thickness at
one side of the test specimen was obtained from the difference
between the observed weight and the initial weight. Test specimens
having an average decrease in thickness of 14 .mu.m or less were
evaluated as having high atmospheric corrosion resistance.
[0079] The weldability of the test specimen was also evaluated. A
y-slit weld cracking test that studies the cold cracking
susceptibility of a welded zone was conducted as the evaluation
method, and the preheating temperature for prevention of weld
cracking was determined. Test specimens having high preheating
temperature for prevention of weld cracking were evaluated as
having low weldability.
[0080] The results of the corrosion test and the results of
evaluation of weldability obtained as above are shown in Table 2
along with the compositions.
[0081] In our Examples (steel type Nos. 1 to 25), the decrease in
thickness was 11.8 to 13.8 .mu.m and high atmospheric corrosion
resistance was exhibited. Although No. 25 has high atmospheric
corrosion resistance, Pcm was more than 0.25 mass %. Thus, the
preheating temperature for prevention of weld cracking was as high
as 100.degree. C. and the weldability was low.
[0082] In particular, steel type No. 7 containing both Nb and Sn
has significantly improved atmospheric corrosion resistance
compared to steel type Nos. 2 and 5 that contain substantially the
same amounts of Cu, Ni, and W and Nb or Sn, where only one of Nb
and Sn is contained. Similarly, steel type No. 8 containing both Nb
and Sn has significantly improved atmospheric corrosion resistance
compared to steel types 1 and 4. Similarly, steel type Nos. 11 and
12 containing both Nb and Sn have improved atmospheric corrosion
resistance compared to steel type 10.
[0083] In contrast, Comparative Examples (steel type Nos. 26 to 42)
outside our range have a decrease in thickness of 14.3 to 17.7
.mu.m and are thus inferior to our Examples in terms of atmospheric
corrosion resistance. Although Comparative Examples (steel type
Nos. 41 and 42) have a decrease in thickness of 14.0 .mu.m and 12.5
.mu.m, respectively, and thus have high atmospheric corrosion
resistance, the alloy cost is high due to a large amount of Ni and
thus the price of the steel material is high. Comparative Example
steel type No. 42 has Pcm exceeding 0.25 mass % and thus the
preheating temperature for prevention of weld cracking was as high
as 100.degree. C., resulting in low weldability.
TABLE-US-00001 TABLE 1 (mass %) Steel Sol type C Si Mn P S Al N O
Ca Cu Ni A 0.088 0.21 0.70 0.020 0.0034 0.024 0.0028 0.0020 0.0001
0.31 0.20 B 0.091 0.19 0.74 0.020 0.0037 0.032 0.0026 0.0017 0.0003
0.32 0.21 C 0.090 0.20 0.74 0.020 0.0036 0.020 0.0023 0.0024 0.0004
0.32 0.21 D 0.094 0.19 0.74 0.020 0.0033 0.030 0.0025 0.0012 0.0001
0.32 0.21 E 0.090 0.19 0.72 0.019 0.0038 0.053 0.0026 0.0019 0.0002
0.31 0.21 F 0.092 0.19 0.72 0.021 0.0043 0.027 0.0030 0.0025 0.0001
0.31 0.21 G 0.088 0.18 0.72 0.019 0.0040 0.029 0.0023 0.0018 0.0001
0.30 0.20 H 0.088 0.18 0.72 0.021 0.0038 0.032 0.0026 0.0015 0.0003
0.30 0.21 I 0.089 0.18 0.71 0.017 0.0036 0.052 0.0026 0.0020 0.0001
0.30 0.20 J 0.091 0.19 0.72 0.019 0.0037 0.033 0.0029 0.0015 0.0007
0.30 0.20 K 0.088 0.19 0.70 0.020 0.0042 0.019 0.0034 0.0020 0.0009
0.31 0.20 L 0.087 0.18 0.71 0.017 0.0038 0.045 0.0029 0.0018 0.0001
0.30 0.20 M 0.090 0.19 0.73 0.021 0.0044 0.020 0.0040 0.0030 0.0001
0.30 0.20 N 0.092 0.19 0.71 0.021 0.0038 0.043 0.0026 0.0013 0.0002
0.30 0.21 O 0.089 0.18 0.72 0.020 0.0032 0.021 0.0030 0.0016 0.0002
0.30 0.20 P 0.099 0.18 0.70 0.018 0.0036 0.045 0.0023 0.0015 0.0001
0.30 0.20 Q 0.095 0.20 0.69 0.019 0.0033 0.028 0.0025 0.0017 0.0005
0.30 0.19 R 0.091 0.18 0.71 0.019 0.0034 0.027 0.0034 0.0013 0.0001
0.30 0.20 S 0.094 0.19 0.69 0.018 0.0033 0.028 0.0026 0.0022 0.0002
-- -- T 0.089 0.19 0.73 0.021 0.0042 0.024 0.0025 0.0013 0.0001
0.02 1.53 U 0.091 0.23 0.69 0.018 0.0038 0.021 0.0027 0.0016 0.0002
0.29 0.21 V 0.087 0.24 0.67 0.017 0.0031 0.025 0.0028 0.0017 0.0001
0.30 0.19 W 0.088 0.17 0.71 0.016 0.0031 0.026 0.0026 0.0018 0.0002
0.31 0.20 X 0.090 0.19 0.72 0.019 0.0032 0.031 0.0026 0.0018 0.0001
0.33 0.21 (mass %) Steel type W Nb Sn Cr Sb Zr Mo P.sub.cm A 0.55
-- -- -- -- -- -- 0.15 B 0.49 -- -- -- 0.10 -- -- 0.15 C 0.54 0.053
-- -- -- -- 0.15 D 0.55 0.052 -- -- -- -- -- 0.16 E 0.44 -- -- --
-- 0.057 -- 0.15 F 0.45 -- -- 0.51 -- -- -- 0.18 G -- -- 0.053 --
0.10 -- -- 0.15 H -- 0.051 -- -- 0.10 -- -- 0.15 I -- -- -- -- 0.10
0.071 -- 0.15 J -- -- -- 0.51 0.10 -- -- 0.18 K -- 0.050 0.051 --
-- -- -- 0.15 L -- -- 0.049 -- -- 0.074 -- 0.15 M -- -- 0.050 0.50
-- -- -- 0.18 N -- 0.050 -- -- -- 0.074 -- 0.15 O -- 0.051 -- 0.50
-- -- -- 0.17 P -- -- -- 0.51 -- 0.085 -- 0.18 Q -- -- -- 0.51 --
-- -- 0.18 R -- -- -- -- -- -- -- 0.15 S -- -- -- -- -- -- -- 0.13
T -- -- -- -- -- -- 0.29 0.16 U 0.25 -- -- -- -- -- -- 0.15 V 0.24
0.029 -- -- -- -- -- 0.15 W 0.21 -- 0.035 -- -- -- -- 0.15 X 0.23
0.012 0.025 -- -- -- -- 0.15 P.sub.cm = [C] + [Si]/30 + [Mn]/20 +
[Cu]/20 + [Ni]/60 + [Cr]/20 + [Mo]/15 + [V]/10 + 5 .times. [B]
TABLE-US-00002 TABLE 2 Steel Composition (mass %) type Sol No. C Si
Mn P S Al N O Ca Cu Ni W Nb Sn Cr Co 1 0.094 0.19 0.74 0.020 0.0033
0.030 0.0025 0.0012 0.0001 0.32 0.21 0.55 0.052 -- -- -- 2 0.087
0.24 0.67 0.017 0.0031 0.025 0.0028 0.0017 0.0001 0.30 0.19 0.24
0.029 -- -- -- 3 0.097 0.20 0.70 0.020 0.0032 0.033 0.0024 0.0013
0.0001 0.29 0.19 0.10 0.012 -- -- -- 4 0.090 0.20 0.74 0.020 0.0036
0.020 0.0023 0.0024 0.0004 0.32 0.21 0.54 -- 0.053 -- -- 5 0.088
0.17 0.71 0.016 0.0031 0.026 0.0026 0.0018 0.0002 0.31 0.20 0.21 --
0.035 -- -- 6 0.096 0.23 0.71 0.018 0.0029 0.025 0.0031 0.0016
0.0002 0.32 0.23 0.19 -- 0.029 -- -- 7 0.081 0.17 0.69 0.016 0.0026
0.037 0.0033 0.0024 0.0001 0.34 0.19 0.23 0.014 0.033 -- -- 8 0.093
0.21 0.71 0.019 0.0031 0.024 0.0029 0.0015 0.0001 0.32 0.20 0.53
0.050 0.054 -- -- 9 0.099 0.19 0.71 0.016 0.0030 0.026 0.0027
0.0020 0.0002 0.30 0.24 0.22 0.023 -- 0.51 -- 10 0.081 0.18 0.70
0.020 0.0031 0.030 0.0022 0.0019 0.0002 0.32 0.23 0.31 -- 0.024
0.41 -- 11 0.098 0.19 0.71 0.012 0.0036 0.028 0.0034 0.0011 0.0007
0.29 0.20 0.21 0.015 0.018 0.40 -- 12 0.093 0.22 0.71 0.014 0.0025
0.038 0.0031 0.0021 0.0001 0.25 0.19 0.48 0.054 0.048 0.55 -- 13
0.090 0.23 0.71 0.021 0.0017 0.025 0.0027 0.0013 0.0001 0.26 0.21
0.24 0.015 -- -- 0.23 14 0.087 0.17 0.72 0.021 0.0037 0.032 0.0031
0.0017 0.0001 0.35 0.24 0.62 -- 0.018 -- -- Preheating Steel Pcm
Decrease temperature for type Composition (mass %) (mass in thick-
prevention of No. Mo Sb REM Ti V Zr B Mg %) ness (.mu.m) cracking
(.degree. C.) Reference 1 -- -- -- -- -- -- -- -- 0.16 13.0 Room
temperature Invention Example 2 -- -- -- -- -- -- -- -- 0.15 13.6
Room temperature Invention Example 3 -- -- -- -- -- -- -- -- 0.16
13.8 Room temperature Invention Example 4 -- -- -- -- -- -- -- --
0.15 13.1 Room temperature Invention Example 5 -- -- -- -- -- -- --
-- 0.15 13.7 Room temperature Invention Example 6 -- -- -- -- -- --
-- -- 0.16 13.8 Room temperature Invention Example 7 -- -- -- -- --
-- -- -- 0.14 12.7 Room temperature Invention Example 8 -- -- -- --
-- -- -- -- 0.15 12.1 Room temperature Invention Example 9 -- 0.042
0.0067 -- -- -- -- -- 0.19 12.3 Room temperature Invention Example
10 -- -- -- -- -- -- -- -- 0.16 12.4 Room temperature Invention
Example 11 -- -- -- -- -- -- -- -- 0.18 12.3 Room temperature
Invention Example 12 -- -- -- -- -- -- -- -- 0.18 12.1 Room
temperature Invention Example 13 -- -- -- -- -- -- -- -- 0.15 12.5
Room temperature Invention Example 14 0.131 -- -- -- -- -- -- --
0.16 12.3 Room temperature Invention Example Steel Composition
(mass %) type Sol No. C Si Mn P S Al N O Ca Cu Ni W Nb Sn Cr Co 15
0.081 0.23 0.72 0.018 0.0037 0.033 0.0026 0.0014 0.0003 0.28 0.24
0.34 0.028 -- -- -- 16 0.095 0.22 0.72 0.019 0.0037 0.038 0.0024
0.0025 0.0001 0.28 0.22 0.27 -- 0.063 -- -- 17 0.084 0.19 0.69
0.013 0.0023 0.028 0.0029 0.0013 0.0001 0.29 0.18 0.42 0.046 --
0.47 0.18 18 0.085 0.17 0.71 0.014 0.0020 0.027 0.0024 0.0024
0.0009 0.25 0.18 0.31 -- 0.042 0.57 -- 19 0.090 0.21 0.72 0.022
0.0027 0.039 0.0021 0.0014 0.0002 0.28 0.20 0.31 0.017 0.028 0.51
-- 20 0.091 0.21 0.71 0.019 0.0038 0.028 0.0033 0.0013 0.0001 0.26
0.18 0.08 0.022 0.034 -- -- 21 0.080 0.19 0.70 0.015 0.0026 0.023
0.0028 0.0017 0.0005 0.34 0.19 0.23 0.011 -- 0.33 -- 22 0.095 0.20
0.70 0.019 0.0040 0.039 0.0033 0.0011 0.0001 0.30 0.22 0.31 --
0.022 -- 0.12 23 0.083 0.17 0.71 0.017 0.0024 0.039 0.0029 0.0011
0.0006 0.26 0.23 0.45 0.047 0.033 0.52 0.26 24 0.099 0.34 0.78
0.013 0.0021 0.023 0.0033 0.0021 0.0003 0.35 0.35 0.31 0.012 0.027
0.13 -- 25 0.131 0.28 1.37 0.016 0.0038 0.022 0.0031 0.0020 0.0002
0.65 0.59 0.23 0.034 -- 0.31 -- 26 0.094 0.19 0.69 0.018 0.0033
0.028 0.0026 0.0022 0.0002 -- -- -- -- -- -- -- 27 0.091 0.18 0.71
0.019 0.0034 0.027 0.0034 0.0013 0.0001 0.30 0.20 -- -- -- -- -- 28
0.088 0.21 0.70 0.020 0.0034 0.024 0.0028 0.0020 0.0001 0.31 0.20
0.55 -- -- -- -- Preheating Steel Pcm Decrease temperature for type
Composition (mass %) (mass in thick- prevention of No. Mo Sb REM Ti
V Zr B Mg %) ness (.mu.m) cracking (.degree. C.) Reference 15 -- --
-- 0.033 -- -- -- -- 0.14 12.5 Room temperature Invention Example
16 -- 0.051 -- -- -- -- -- -- 0.16 12.4 Room temperature Invention
Example 17 -- -- -- -- 0.021 -- -- -- 0.17 12.0 Room temperature
Invention Example 18 0.332 -- 0.0221 -- -- -- -- -- 0.19 12.1 Room
temperature Invention Example 19 0.165 0.046 -- -- -- 0.043 -- --
0.19 11.9 Room temperature Invention Example 20 -- 0.055 -- -- --
-- -- 0.0024 0.15 12.3 Room temperature Invention Example 21 -- --
0.0743 -- -- -- 0.0052 -- 0.18 12.2 Room temperature Invention
Example 22 -- 0.034 -- 0.011 -- 0.032 0.0031 -- 0.17 12.4 Room
temperature Invention Example 23 0.258 -- 0.031 -- 0.043 -- --
0.0037 0.19 11.8 Room temperature Invention Example 24 -- -- -- --
-- -- -- -- 0.18 12.3 Room temperature Invention Example 25 -- --
-- -- -- -- 0.27 11.9 100.degree. C. Invention Example 26 -- -- --
-- -- -- -- -- 0.13 17.2 Room temperature Comparative Example 27 --
-- -- -- -- -- -- -- 0.15 15.2 Room temperature Comparative Example
28 -- -- -- -- -- -- -- -- 0.15 15.4 Room temperature Comparative
Example Steel Composition (mass %) type Sol No. C Si Mn P S Al N O
Ca Cu Ni W Nb Sn Cr Co 29 0.095 0.20 0.70 0.019 0.0035 0.023 0.0026
0.0010 0.0002 0.30 0.19 -- 0.071 -- -- -- 30 0.093 0.20 0.70 0.018
0.0034 0.022 0.0027 0.0014 0.0001 0.30 0.20 -- -- 0.053 -- -- 31
0.095 0.20 0.69 0.019 0.0033 0.028 0.0025 0.0017 0.0005 0.30 0.19
-- -- -- 0.51 -- 32 0.093 0.20 0.70 0.015 0.0039 0.037 0.0021
0.0023 0.0002 0.34 0.21 0.21 0.002 -- -- -- 33 0.097 0.21 0.71
0.021 0.0033 0.022 0.0033 0.0011 0.0001 0.33 0.19 0.33 -- 0.003 --
-- 34 0.092 0.20 0.70 0.018 0.0015 0.035 0.0029 0.0018 0.0001 0.31
0.21 0.02 0.018 0.043 -- -- 35 0.092 0.19 0.72 0.021 0.0043 0.027
0.0030 0.0025 0.0001 0.31 0.21 0.45 -- -- 0.51 -- 36 0.087 0.19
0.73 0.020 0.0038 0.030 0.0027 0.0016 0.0002 0.31 0.20 0.51 -- --
-- -- 37 0.095 0.23 0.72 0.021 0.0035 0.028 0.0026 0.0017 0.0003
0.25 0.23 0.29 -- -- -- -- 38 0.095 0.18 0.69 0.019 0.0035 0.028
0.0026 0.0019 0.0002 0.32 0.20 0.31 -- -- -- -- 39 0.088 0.19 0.70
0.020 0.0042 0.019 0.0034 0.0020 0.0009 0.31 0.20 -- 0.050 0.051 --
-- 40 0.089 0.18 0.72 0.020 0.0032 0.021 0.0030 0.0016 0.0002 0.30
0.20 -- 0.051 -- 0.50 -- 41 0.089 0.19 0.73 0.021 0.0042 0.024
0.0025 0.0013 0.0001 0.02 1.53 -- -- -- -- -- 42 0.098 0.25 0.91
0.018 0.0033 0.028 0.0035 0.0014 0.0003 0.91 2.41 -- -- -- 0.59 --
Preheating Steel Pcm Decrease temperature for type Composition
(mass %) (mass in thick- prevention of No. Mo Sb REM Ti V Zr B Mg
%) ness (.mu.m) cracking (.degree. C.) Reference 29 -- -- -- -- --
-- -- -- 0.15 15.3 Room temperature Comparative Example 30 -- -- --
-- -- -- -- -- 0.15 17.7 Room temperature Comparative Example 31 --
-- -- -- -- -- -- -- 0.18 14.3 Room temperature Comparative Example
32 -- -- -- -- -- -- -- -- 0.15 15.5 Room temperature Comparative
Example 33 -- -- -- -- -- -- -- -- 0.16 15.2 Room temperature
Comparative Example 34 -- -- -- -- -- -- -- -- 0.15 15.0 Room
temperature Comparative Example 35 -- -- -- -- -- -- -- -- 0.18
14.6 Room temperature Comparative Example 36 0.493 -- -- -- 0.038
-- -- -- 0.19 14.7 Room temperature Comparative Example 37 -- 0.070
-- -- -- -- -- 0.0021 0.15 15.0 Room temperature Comparative
Example 38 -- -- -- -- -- 0.043 0.0015 -- 0.16 14.9 Room
temperature Comparative Example 39 -- -- -- -- -- -- -- -- 0.15
15.0 Room temperature Comparative Example 40 -- -- -- -- -- -- --
-- 0.17 14.9 Room temperature Comparative Example 41 0.291 -- -- --
-- -- -- -- 0.18 14.0 Room temperature Comparative Example 42 -- --
-- -- -- -- 0.27 12.5 100.degree. C. Comparative Example P.sub.cm =
[C] + [Si]/30 + [Mn]/20 + [Cu]/20 + [Ni]/60 + [Cr]/20 + [Mo]/15 +
[V]/10 + 5 .times. [B]
* * * * *